Solar Hot Water (Solar Thermal) Systems

Using solar power to heat your water is one of the most practical and cost effective ways to harness energy from the sun. Solar thermal systems absorb the sun’s heat and use it to heat your residence’s own hot water needs. In general, the solar thermal system will easily heat water to 140ºF or higher matching the range of its traditional hot water tank counterpart. Effective systems can collect up to 70 percent of the sun’s energy that reaches them and transfer it to you.

How Solar Hot Water Heating Systems Work

In general there are two types of active water heating systems: direct and indirect.

Direct Solar Water Heating

As implied, direct systems capture the sun’s heat in collectors to directly heat a household’s water supply. The system consists of collector pipes filled with water that are linked to an insulated storage tank usually located inside a home. As the sun heats the water inside the pipes, the water flows into the storage tank. Although direct systems are more efficient that indirect ones, they require more maintenance to keep the pipes clear of mineral deposits. Direct solar thermal systems also work best in warmer climates where the system is less prone to freezing.

Indirect Solar Water Heating

Indirect systems do not heat the water directly rather they use fluid with a low-freezing point to absorb radiant energy from the sun. Also termed closed-loop systems, an indirect solar water heating system absorbs the sun’s rays into heat pipes evacuated of air which in turn heats up the pipe’s thin copper laminate located on the back of each pipe. The collection array consists of multiple heating pipes that are mounted and tilted to maximize solar collection.

Often glycol (an ingredient in antifreeze) runs through adjacent pipes within the array and heats up via contact with the copper laminate. As the temperature in the pipes rise, the heat activates a pump that circulates the glycol fluid through a heat exchange coil in the water tank. That coil, in turn, transfers its heat to the water tank and voila, hot water is produced.

Solar Pool and Hot Tub Heating Systems

Solar pool heating systems work on a similar principle to a direct system solar hot water heater. However, because the water can heat up too much in a solar thermal system, the collector’s glazing is often removed. Using non-glazed pipes or a heating system that resembles a flat black mat prevents the pool water from becoming super-heated as well as reduces costs to the overall system.

While solar pool and hot tub heating systems often are exempted from federal and state monetary solar incentives and rebates, they often pay for themselves within 1–5 years (depending mostly on where you live).

For more information about the costs associated with solar power pool systems refer to our Solar Power Cost page.

Radiant Heating Systems For Your Home

You can also use a solar hot water (or thermal) system to heat your home. Rather than transferring the heated water to a domestic hot water heater, the solar hot water system can connect to a radiant floor and/or wall panel radiator.

You can make the collection and distribution system as simple or complicated as you like depending on your location, climate, and intended use. Most radiant heating systems use the collection array to heat water and store it in a large thermal collection tank so that you have enough heat to last at least throughout the night. A general rule of thumb is to have a collection tank that can store 1½ to 2 gallons of water for every square foot of solar collector. That water, in turn, is piped via plastic tubing under floors to create an effective heating system.

Radiant floor heating systems have many advantages. They are typically 40 percent more efficient than a forced air heating system and can be zoned so that each room has its own thermostat. Furthermore, radiant floors distribute heat beneath your feet where it naturally rises providing a cozy and evenly distributed heated living space.

Solar Hot Water Heater Tips for Cooler Climates

In cooler climates during the colder times of the year, an indirect solar hot water system can help lower your energy costs by working as a water preheating system rather than an outright water heater. Preheated water reduces the load on your other energy systems to heat the water.

Another trick to increase the system’s efficiency is to wrap your water tank with an insulation blanket to keep the water sufficiently warm and further minimize the need to rely on traditional power sources to heat your water. (Note that not all water heaters need an insulation blanket. Many of the newer energy-efficient models come with a thicker layer of insulation inside the tank that eliminates the need for additional insulation).

Where to Place a Solar Thermal Collection System

Like other types of solar energy systems, solar hot water heating systems work best on south-facing walls with full sun exposure. Because of the collector tubes’ type of construction, the outside elements have less effect on its performance compared to a photovoltaic collection system; a bit of shade on the thermal array will have a less noticeable impact.

Work with a Solar Pro

As with any solar power upgrade, consulting with a solar installer can help you evaluate your potential savings and determine the type of solar hot water system that’s best for you. Solar thermal panels come both as stand-alone collection arrays and as integrated building panels. A solar pro can size your system and help you compare the different options for the collection panels and water tank you may need. And remember, solar domestic water systems often qualify for federal, state, and local tax credits and rebates!

For more information about solar hot water system costs, visit our Solar Power Cost page or visit our Solar Power Financing Options page for information on how to pay for your system.